Grapefruit is a library for Functional Reactive Programming (FRP) with a focus on user interfaces. FRP makes it possible to implement reactive and interactive systems in a declarative style. With Grapefruit, user interfaces are described as networks of communicating widgets and windows. Communication is done via different kinds of signals which describe temporal behavior.

Scion is a library that aims to provide IDE-like functionality on top of the GHC API. It aims to be front-end agnostic, thus serve as a common middle-layer for various Haskell programming frontends like Emacs, Vim, Yi, Eclipse, etc.

It currently only provides rudimentary functionality, such as loading a project and single-threaded background-typechecking. Currently, Scion's only frontend is Emacs, but a Vim frontend is in the underway. Possible Hackathon projects could be:

Update (Sun Dec 13 22:20:03 CET 2009): Vim is supported and scion is that useful that you shouldn't miss it. There are still some features lacking which Eclipse etc provide. You should definitely give it a try!

Type class aliases is a much wanted extension to Haskell proposed long ago by John Meacham (John's website, mailing list) that has never been implemented yet. It is time this extension sees the light of day!